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  Gitee
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2021
</a></span></div></div> <div data-v-2d5f533b><main class="page"><div class="page-title" style="display:none;"><h1 class="title">函数</h1> <div data-v-3b7f5bdf><i class="iconfont reco-account" data-v-3b7f5bdf><span data-v-3b7f5bdf>pgmanor</span></i> <i class="iconfont reco-date" data-v-3b7f5bdf><span data-v-3b7f5bdf>2021-01-01</span></i> <i class="iconfont reco-eye" data-v-3b7f5bdf><span id="/manor-farm-mysql/zh/guide/essentials/e-11-function.html" data-flag-title="Your Article Title" class="leancloud-visitors" data-v-3b7f5bdf><a class="leancloud-visitors-count" style="font-size:.9rem;font-weight:normal;color:#999;"></a></span></i> <i class="iconfont reco-tag tags" data-v-3b7f5bdf><span class="tag-item" data-v-3b7f5bdf>function</span></i></div></div> <div class="theme-reco-content content__default" style="display:none;"><p>本文主要介绍下mysql的常用函数和自定义函数</p> <p>mysql的函数特别多，不可能都介绍到，只介绍一些常用的函数。已经自己如何自定义函数。</p> <div id="boxx" data-v-f4ca0dac><div data-v-f4ca0dac><p v-if="true" class="custom-block-title" data-v-f4ca0dac></p> <p v-if="true" data-v-f4ca0dac></p></div></div> <h2 id="_1-系统函数">1.系统函数</h2> <h3 id="_1-1-字符串">1-1.字符串</h3> <p><strong>CONCAT</strong> : 字符串拼接</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> concat<span class="token punctuation">(</span><span class="token string">'pgmanor'</span><span class="token punctuation">,</span> <span class="token string">'@qq.com'</span><span class="token punctuation">)</span> <span class="token keyword">from</span> dual<span class="token punctuation">;</span> 
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p><strong>CONCAT_WS</strong>: 字符串长度，之间使用符号分割</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> concat_ws<span class="token punctuation">(</span><span class="token string">','</span><span class="token punctuation">,</span> <span class="token string">'小爱'</span><span class="token punctuation">,</span> <span class="token string">'酷飞'</span><span class="token punctuation">,</span> <span class="token string">'乐迪'</span><span class="token punctuation">)</span> <span class="token keyword">from</span> dual<span class="token punctuation">;</span> 
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p><strong>CHAR_LENGTH</strong>: 字符串长度</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> char_length<span class="token punctuation">(</span><span class="token string">'pgmanor'</span><span class="token punctuation">)</span> <span class="token keyword">from</span> dual<span class="token punctuation">;</span> 

<span class="token comment">-- 结果 abc 7</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p><strong>LEFT(s,n)</strong>: 字符串 s 的前 n 个字符</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> <span class="token keyword">left</span><span class="token punctuation">(</span><span class="token string">'abcdef'</span><span class="token punctuation">,</span><span class="token number">3</span><span class="token punctuation">)</span> <span class="token keyword">from</span> dual<span class="token punctuation">;</span> 

<span class="token comment">-- 结果 abc</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p><strong>RIGHT(s,n)</strong>: 字符串 s 的后 n 个字符</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> <span class="token keyword">left</span><span class="token punctuation">(</span><span class="token string">'abcdef'</span><span class="token punctuation">,</span><span class="token number">3</span><span class="token punctuation">)</span> <span class="token keyword">from</span> dual<span class="token punctuation">;</span> 

<span class="token comment">-- 结果 def</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p><strong>LOWER</strong>: 转化为小写</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> lower<span class="token punctuation">(</span><span class="token string">'ABcdEF'</span><span class="token punctuation">)</span> <span class="token keyword">from</span> dual<span class="token punctuation">;</span> 

<span class="token comment">-- 结果 abcdef</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p><strong>UPPER</strong>: 转化为大写写</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> upper<span class="token punctuation">(</span><span class="token string">'ABcdEF'</span><span class="token punctuation">)</span> <span class="token keyword">from</span> dual<span class="token punctuation">;</span> 

<span class="token comment">-- 结果 ABCDEF</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p><strong>LPAD(s1,len,s2)</strong>: 在字符串 s1 的开始处填充字符串 s2，使字符串长度达到 len</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> lpad<span class="token punctuation">(</span><span class="token string">'1234'</span><span class="token punctuation">,</span> <span class="token number">6</span><span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token keyword">from</span> dual<span class="token punctuation">;</span> 

<span class="token comment">-- 结果 001234</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p><strong>RPAD(s1,len,s2)</strong>： 在字符串 s1 的结尾处添加字符串 s2，使字符串的长度达到 len</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> rpad<span class="token punctuation">(</span><span class="token string">'1234'</span><span class="token punctuation">,</span> <span class="token number">6</span><span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token keyword">from</span> dual<span class="token punctuation">;</span> 

<span class="token comment">-- 结果 123400</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p><strong>REPEAT(s,n)</strong>	: 将字符串 s 重复 n 次</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> <span class="token keyword">repeat</span><span class="token punctuation">(</span><span class="token string">'abc'</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">)</span> <span class="token keyword">from</span> dual<span class="token punctuation">;</span>
<span class="token comment">-- 结果 abcabcabc </span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p><strong>SUBSTRING(s, start, length)</strong>: 从字符串 s 的 start 位置截取长度为 length 的子字符串</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> <span class="token keyword">repeat</span><span class="token punctuation">(</span><span class="token string">'abcdef'</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">)</span> <span class="token keyword">from</span> dual<span class="token punctuation">;</span>

<span class="token comment">-- 结果 cd </span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><blockquote><p>从1开始计数</p></blockquote> <p><strong>COALESCE(expr1, expr2, ...., expr_n)</strong>： 返回参数中的第一个非空表达式（从左向右）</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> ename <span class="token punctuation">,</span> <span class="token keyword">coalesce</span><span class="token punctuation">(</span>comm<span class="token punctuation">,</span><span class="token string">'没福利'</span><span class="token punctuation">)</span> <span class="token keyword">as</span> comm <span class="token keyword">from</span> emp<span class="token punctuation">;</span>

</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>等价于</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">SELECT</span> ename
     <span class="token punctuation">,</span> <span class="token keyword">CASE</span>
           <span class="token keyword">WHEN</span> comm <span class="token operator">IS</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span> <span class="token keyword">THEN</span> comm
           <span class="token keyword">ELSE</span>
               <span class="token string">'没福利'</span> <span class="token keyword">END</span> <span class="token keyword">as</span> comm
<span class="token keyword">FROM</span> emp<span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><div class="custom-block warning"><p class="custom-block-title">注意</p> <p>在select字段中可以使用coalesce，但是在where别使用该函数。会全表扫描，具体后面千锤百炼章节会介绍。</p></div> <h3 id="_1-2-数字">1-2.数字</h3> <p><strong>ABS(x)</strong>: 绝对值</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> abs<span class="token punctuation">(</span><span class="token operator">-</span><span class="token number">2</span><span class="token punctuation">)</span> <span class="token keyword">from</span> dual<span class="token punctuation">;</span>

<span class="token comment">-- 结果： 2</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p><strong>FLOOR(x)</strong>: 小于或等于 x 的最大整数</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> floor<span class="token punctuation">(</span><span class="token number">4.8</span><span class="token punctuation">)</span> <span class="token keyword">from</span> dual<span class="token punctuation">;</span>

<span class="token comment">-- 结果： 4</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p><strong>CEIL(x)</strong>: 大于或等于 x 的最小整数</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> ceil <span class="token punctuation">(</span><span class="token number">4.4</span><span class="token punctuation">)</span> <span class="token keyword">from</span> dual<span class="token punctuation">;</span>

<span class="token comment">-- 结果： 5</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p><strong>MIN(expression)</strong>	: 最小值</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> <span class="token function">min</span><span class="token punctuation">(</span>age<span class="token punctuation">)</span> <span class="token keyword">from</span> student<span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p><strong>MAX(expression)</strong>	: 最大值</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> <span class="token function">max</span><span class="token punctuation">(</span>age<span class="token punctuation">)</span> <span class="token keyword">from</span> student<span class="token punctuation">;</span>

<span class="token comment">-- 结果： 2</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p><strong>RAND()</strong>: 0-1之间随机</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> rand<span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token operator">*</span><span class="token number">10</span> <span class="token keyword">from</span> dual<span class="token punctuation">;</span>

<span class="token comment">-- 随机结果：0.026489562379652228</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p><strong>SUM(expression)</strong>	: 求和</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> <span class="token function">sum</span><span class="token punctuation">(</span>age<span class="token punctuation">)</span> <span class="token keyword">from</span> student<span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p><strong>m DIV n</strong>	: m除以n</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> <span class="token number">3</span> <span class="token operator">div</span> <span class="token number">2</span>  <span class="token keyword">as</span> <span class="token string">'结果'</span> <span class="token keyword">from</span> dual<span class="token punctuation">;</span>

<span class="token comment">-- 结果： 1</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p><strong>MOD(x,y)</strong>: 取余</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> <span class="token function">mod</span><span class="token punctuation">(</span><span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">)</span> <span class="token keyword">from</span> dual<span class="token punctuation">;</span>

<span class="token comment">-- 结果： 1</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><h3 id="_1-3-日期">1-3.日期</h3> <p><strong>NOW()</strong> 或 <strong>CURRENT_TIMESTAMP()</strong>: 当前日期和时间</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> <span class="token function">NOW</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">select</span> <span class="token keyword">CURRENT_TIMESTAMP</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token comment">-- 2021-01-01 18:58:26.0</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><p><strong>CURDATE()</strong> 或 <strong>CURRENT_DATE()</strong>	:当前日期</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> CURDATE<span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">select</span> <span class="token keyword">CURRENT_DATE</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token comment">-- 2021-01-01</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><p><strong>CURTIME</strong> 或 <strong>CURRENT_TIME</strong> ：当前时间</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> CURTIME<span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">select</span> <span class="token keyword">CURRENT_TIME</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token comment">-- 19:05:27</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><p><strong>DATEDIFF(d1,d2)</strong>：计算日期 d1-&gt;d2 之间相隔的天数</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">SELECT</span> DATEDIFF<span class="token punctuation">(</span><span class="token string">'2021-01-01'</span><span class="token punctuation">,</span><span class="token string">'2021-02-02'</span><span class="token punctuation">)</span>

<span class="token comment">-- -32</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><blockquote><p>可能为正数也可能为负数</p></blockquote> <p><strong>DATE_ADD(d，INTERVAL expr type)</strong>： 计算起始日期 d 加上一个时间段后的日期	
<strong>DATE_SUB(d，INTERVAL expr type)</strong>： 函数从日期减去指定的时间间隔。</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">SELECT</span>  DATE_ADD<span class="token punctuation">(</span><span class="token string">'2021-01-01'</span><span class="token punctuation">,</span> <span class="token keyword">INTERVAL</span> <span class="token number">1</span> week<span class="token punctuation">)</span> <span class="token keyword">from</span> DUAL<span class="token punctuation">;</span>
<span class="token keyword">SELECT</span>  DATE_ADD<span class="token punctuation">(</span><span class="token string">'2021-01-01'</span><span class="token punctuation">,</span> <span class="token keyword">INTERVAL</span> <span class="token operator">-</span><span class="token number">1</span> <span class="token keyword">MONTH</span><span class="token punctuation">)</span> <span class="token keyword">from</span> DUAL<span class="token punctuation">;</span>

<span class="token keyword">SELECT</span>  DATE_SUB<span class="token punctuation">(</span><span class="token string">'2021-01-01'</span><span class="token punctuation">,</span> <span class="token keyword">INTERVAL</span> <span class="token number">1</span> <span class="token keyword">MONTH</span><span class="token punctuation">)</span> <span class="token keyword">from</span> DUAL<span class="token punctuation">;</span>
<span class="token keyword">SELECT</span>  DATE_SUB<span class="token punctuation">(</span><span class="token string">'2021-01-01'</span><span class="token punctuation">,</span> <span class="token keyword">INTERVAL</span> <span class="token number">1</span> QUARTER<span class="token punctuation">)</span> <span class="token keyword">from</span> DUAL<span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><p><strong>type: 常用的几个值</strong></p> <table><thead><tr><th>类型</th> <th>描述</th></tr></thead> <tbody><tr><td>SECOND</td> <td>秒</td></tr> <tr><td>MINUTE</td> <td>分</td></tr> <tr><td>HOUR</td> <td>时</td></tr> <tr><td>DAY</td> <td>天</td></tr> <tr><td>WEEK</td> <td>周</td></tr> <tr><td>MONTH</td> <td>月</td></tr> <tr><td>QUARTER</td> <td>季</td></tr> <tr><td>YEAR</td> <td>年</td></tr></tbody></table> <p><strong>DAYOFMONTH</strong>： 计算日期 d 是本月的第几天
<strong>DAYOFYEAR(d)</strong>: 计算日期 d 是本年的第几天	
<strong>DAYOFWEEK(d)</strong>: 日期 d 今天是星期几，1 星期日，2 星期一</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">SELECT</span>  dayofmonth<span class="token punctuation">(</span><span class="token string">'2021-01-01'</span><span class="token punctuation">)</span> <span class="token keyword">from</span> DUAL<span class="token punctuation">;</span>
<span class="token comment">-- 一月第一个天</span>

<span class="token keyword">SELECT</span>  dayofweek<span class="token punctuation">(</span><span class="token string">'2021-01-01'</span><span class="token punctuation">)</span> <span class="token keyword">from</span> DUAL<span class="token punctuation">;</span>
<span class="token comment">-- 6：星期五。(星期日：0，星期一: 1 ...)</span>

<span class="token keyword">SELECT</span>  dayofyear<span class="token punctuation">(</span><span class="token string">'2021-01-01'</span><span class="token punctuation">)</span> <span class="token keyword">from</span> DUAL<span class="token punctuation">;</span>
<span class="token comment">-- 一年第一个天</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div><p><strong>DATE_FORMAT(d,f)</strong>: 按表达式 f的要求显示日期 d</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">SELECT</span> DATE_FORMAT<span class="token punctuation">(</span><span class="token function">now</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token string">'%Y-%c-%d %h:%i:%s'</span><span class="token punctuation">)</span> <span class="token keyword">FROM</span> dual<span class="token punctuation">;</span>
<span class="token comment">-- 2021-01-01 07:25:05</span>

<span class="token keyword">SELECT</span> DATE_FORMAT<span class="token punctuation">(</span><span class="token function">now</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token string">'%Y-%c-%d'</span><span class="token punctuation">)</span> <span class="token keyword">FROM</span> dual<span class="token punctuation">;</span>

<span class="token comment">-- 2021-01-01</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><h2 id="_2-自定义函数">2.自定义函数</h2> <p>上面我们都介绍的时系统提供的函数，如果系统函数不能满足我们，我们还可以自定义函数。</p> <h3 id="_2-1-语法">2-1.语法</h3> <p><strong>创建函数</strong></p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">CREATE</span> <span class="token keyword">FUNCTION</span> 函数名<span class="token punctuation">(</span>参数列表<span class="token punctuation">)</span> <span class="token keyword">RETURNS</span> 返回类型
<span class="token keyword">BEGIN</span>
	函数体
<span class="token keyword">END</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><p><strong>调用函数</strong></p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">SELECT</span> 函数名<span class="token punctuation">(</span>参数列表<span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p><strong>查看函数</strong></p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">SHOW</span> <span class="token keyword">FUNCTION</span> 函数名<span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p><strong>删除函数</strong></p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">DROP</span> <span class="token keyword">FUNCTION</span> <span class="token keyword">IF</span> <span class="token keyword">EXISTS</span> 函数名<span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><h3 id="_2-2-示例">2-2.示例</h3> <p><strong>根据姓名查询邮件</strong></p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">DROP</span> <span class="token keyword">FUNCTION</span> <span class="token keyword">IF</span> <span class="token keyword">EXISTS</span> getEmaiLByName<span class="token punctuation">;</span>

<span class="token comment">-- 自定义结束符 $</span>
<span class="token keyword">DELIMITER</span> $

<span class="token keyword">CREATE</span> <span class="token keyword">FUNCTION</span> getEmaiLByName<span class="token punctuation">(</span>p_name <span class="token keyword">VARCHAR</span><span class="token punctuation">(</span><span class="token number">20</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token keyword">RETURNS</span> <span class="token keyword">VARCHAR</span>
<span class="token keyword">BEGIN</span>
    <span class="token comment">-- 定义变量</span>
	<span class="token keyword">SET</span> l_var_email<span class="token operator">=</span><span class="token string">''</span><span class="token punctuation">;</span>
	<span class="token keyword">SELECT</span> email <span class="token keyword">INTO</span> l_var_email
	<span class="token keyword">FROM</span> student
	<span class="token keyword">WHERE</span> name <span class="token operator">=</span> p_name<span class="token punctuation">;</span>
	
	<span class="token keyword">RETURN</span> l_var_email<span class="token punctuation">;</span>
<span class="token keyword">END</span> $

<span class="token comment">-- 恢复结束符 ;</span>
<span class="token keyword">DELIMITER</span> <span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br></div></div><p><strong>如果创建函数报以下错误</strong></p> <blockquote><p>SQL 错误 [1418] [HY000]: This function has none of DETERMINISTIC, NO SQL,
or READS SQL DATA in its declaration and binary logging is enabled
(you <em>might</em> want to use the less safe log_bin_trust_function_creators variable)</p></blockquote> <p><strong>解决方法</strong></p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">set</span> <span class="token keyword">global</span> log_bin_trust_function_creators<span class="token operator">=</span><span class="token boolean">TRUE</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p><strong>调用</strong></p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> getEmaiLByName<span class="token punctuation">(</span><span class="token string">'pgmanor_1'</span><span class="token punctuation">)</span> <span class="token keyword">as</span> <span class="token string">'邮件'</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p><strong>结果</strong></p> <table><thead><tr><th>邮件</th></tr></thead> <tbody><tr><td>pgmanor1@qq.com</td></tr></tbody></table></div> <footer class="page-edit" style="display:none;"><!----> <div class="last-updated"><span class="prefix">Last Updated: </span> <span class="time">2020-12-20 11:21:37 PM</span></div></footer> <!----> <!----> <!----></main> <!----></div></div></div></div><div class="global-ui"><div class="back-to-ceiling" style="right:1rem;bottom:6rem;width:2.5rem;height:2.5rem;border-radius:.25rem;line-height:2.5rem;display:none;" data-v-c6073ba8 data-v-c6073ba8><svg t="1574745035067" viewBox="0 0 1024 1024" version="1.1" xmlns="http://www.w3.org/2000/svg" p-id="5404" class="icon" data-v-c6073ba8><path d="M526.60727968 10.90185116a27.675 27.675 0 0 0-29.21455937 0c-131.36607665 82.28402758-218.69155461 228.01873535-218.69155402 394.07834331a462.20625001 462.20625001 0 0 0 5.36959153 69.94390903c1.00431239 6.55289093-0.34802892 13.13561351-3.76865779 18.80351572-32.63518765 54.11355614-51.75690182 118.55860487-51.7569018 187.94566865a371.06718723 371.06718723 0 0 0 11.50484808 91.98906777c6.53300375 25.50556257 41.68394495 28.14064038 52.69160883 4.22606766 17.37162448-37.73630017 42.14135425-72.50938081 72.80769204-103.21549295 2.18761121 3.04276886 4.15646224 6.24463696 6.40373557 9.22774369a1871.4375 1871.4375 0 0 0 140.04691725 5.34970492 1866.36093723 1866.36093723 0 0 0 140.04691723-5.34970492c2.24727335-2.98310674 4.21612437-6.18497483 6.3937923-9.2178004 30.66633723 30.70611158 55.4360664 65.4791928 72.80769147 103.21549355 11.00766384 23.91457269 46.15860503 21.27949489 52.69160879-4.22606768a371.15156223 371.15156223 0 0 0 11.514792-91.99901164c0-69.36717486-19.13165746-133.82216804-51.75690182-187.92578088-3.42062944-5.66790279-4.76302748-12.26056868-3.76865837-18.80351632a462.20625001 462.20625001 0 0 0 5.36959269-69.943909c-0.00994388-166.08943902-87.32547796-311.81420293-218.6915546-394.09823051zM605.93803103 357.87693858a93.93749974 93.93749974 0 1 1-187.89594924 6.1e-7 93.93749974 93.93749974 0 0 1 187.89594924-6.1e-7z" p-id="5405" data-v-c6073ba8></path><path d="M429.50777625 765.63860547C429.50777625 803.39355007 466.44236686 1000.39046097 512.00932183 1000.39046097c45.56695499 0 82.4922232-197.00623328 82.5015456-234.7518555 0-37.75494459-36.9345906-68.35043303-82.4922232-68.34111062-45.57627738-0.00932239-82.52019037 30.59548842-82.51086798 68.34111062z" p-id="5406" data-v-c6073ba8></path></svg></div><!----><!----><APlayer audio="" fixed="true" mini="true" theme="#f9bcdd" loop="loop" order="random" preload="auto" volume="0.1" mutex="true" lrc-type="0" list-folded="true" list-max-height="250" storage-name="vuepress-plugin-meting" id="aplayer-fixed"></APlayer></div></div>
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